1. Technical Field
The present disclosure relates to a variable nozzle unit and the like, which adjusts a passage area for (a flow rate of) an exhaust gas to be supplied to a turbine wheel side of a variable geometry turbocharger.
2. Description of the Related Art
A variable geometry turbocharger is equipped with a variable nozzle unit, which adjusts a passage area for (a flow rate of) an exhaust gas to be supplied to a turbine wheel side. Related techniques are illustrated in Japanese Patent Application Publication No. 2009-243431 (PTL 1) and Japanese Patent Application Publication No. 2009-243300 (PTL 2). A specific configuration of a variable nozzle unit according to the related technique is as described below.
Inside a turbine housing, a first nozzle ring serving as an annular first wall member is disposed concentrically with a turbine wheel. Multiple first attachment holes are penetratingly formed (formed in a penetrating manner) in this first nozzle ring at intervals in a circumferential direction (a predetermined circumferential direction). Meanwhile, a second nozzle ring serving as an annular second wall member is provided integrally with the first nozzle ring at a position away in an axial direction (in an axial direction of the turbine wheel) from the first nozzle ring. Multiple second attachment holes are penetratingly formed in this second nozzle ring at intervals in the circumferential direction so as to be aligned with the multiple first attachment holes in the first nozzle ring.
Multiple connecting pins are provided in an integrally connected manner between the first nozzle ring and the second nozzle ring. The multiple connecting pins are arranged at intervals in the circumferential direction (the predetermined circumferential direction). One end portion (one end portion in an axial direction) of each connecting pin is joined in an inserted state to the corresponding first attachment hole in the first nozzle ring. Another end portion (another end portion in the axial direction) of each connecting pin is joined in an inserted state to the corresponding second attachment hole in the second nozzle ring. A side surface on an axially one side of an intermediate portion of each connecting pin comes into contact with an opposed surface of the first nozzle ring. A side surface on an axially other side of the intermediate portion of each connecting pin comes into contact with an opposed surface of the second nozzle ring.
Multiple variable nozzles are disposed at regular intervals in the circumferential direction (the predetermined circumferential direction) between the opposed surface of the first nozzle ring and the opposed surface of the second nozzle ring. Each variable nozzle is turnable in forward and reverse directions (opening and closing directions) around a shaft center (a shaft center of a nozzle shaft of the variable nozzle) which is parallel to a shaft center of the turbine wheel. A link mechanism for turning the multiple variable nozzles synchronously in the forward and reverse directions is disposed in a link chamber that is defined and formed on an opposite surface side from the opposed surface of the first nozzle ring. A passage area (a throat area) for an exhaust gas to be supplied to the turbine wheel side is increased when the multiple variable nozzles are turned synchronously in the forward direction (the opening direction). On the other hand, the passage area for the exhaust gas to be supplied to the turbine wheel side is reduced when the multiple variable nozzles are turned synchronously in the reverse direction (the closing direction).
A support ring having a diameter greater than an outside diameter of the first nozzle ring is provided on the opposite surface from the opposed surface of the first nozzle ring. An inner edge portion (an inner peripheral edge portion) of the support ring is integrally connected by joining of one end portions of the multiple connecting pins. Multiple pin holes (third attachment holes) for allowing insertion of the one end portions of the connecting pins are penetratingly formed in the inner edge portion of the support ring at intervals in the circumferential direction so as to be aligned with the multiple first attachment holes in the first nozzle ring. An outer edge portion (an outer peripheral edge portion) of the support ring is attached to a bearing housing in a sandwiched state in cooperation with the turbine housing.